As is well known to those skilled in the art, a clathrate hydrate or gas hydrate comprises two constituents including host molecules forming a hydrogen-bonded solid lattice structure and guest molecules which are trapped inside the hydrogen-bonded solid lattice structure of the host molecules. For example, the clathrate hydrate or gas hydrate is a crystalline compound in which low molecules, such as methane, ethane, carbon dioxide, etc., are physically trapped, without being chemically bonded, inside a three-dimensional lattice structure formed by the hydrogen bonds of water molecules.
About one hundred thirty kinds of guest molecules which can be trapped in the host molecules of gas hydrates have been discovered to date. CH4, C2H6, C3H8, CO2, H2, SF6, etc. are representative examples of such guest molecules. Furthermore, gas hydrate crystalline structures have a polyhedral cavity formed by the hydrogen bonded host molecules. According to the kind of gas molecule and the formation conditions thereof, the gas hydrate crystalline structures are classified into a body-centered cubic structure I (sI), a diamond cubic structure II (sII) and a hexagonal structure H (sH). In the sI and sII, the size of a guest molecule is the critical factor. In sH, the size and shape of a guest molecule are the critical factors.
FIG. 1 is a view illustrating a conventional gas hydrate reactor.
A water supply unit 1 and a gas supply unit 2 supply water and gas into a mixing chamber 3. The water and gas are mixed with each other in the mixing chamber 3 before being supplied into a reactor 4.
The reactor 4 must generally create a high-pressure and low-temperature environment although it may vary depending on the conditions used to produce the gas hydrate. Here, the pressure in the reactor 4 is adjusted by the supply of gas. The temperature in the reactor 4 is controlled by adjusting the temperature of a water bath 6.
Gas hydrates are formed in the reactor 4.
Meanwhile, an agitator 5 may be used to promote the formation of gas hydrates. Formed gas hydrates are stored in a gas hydrate storage unit 7.
Although a cooling method in which the water bath 6 is used to meet the low temperature conditions in the reactor 4 is illustrated in FIG. 1, a jacket type cooling method in which the reactor 4 is covered with cooling fluid may be used to satisfy the low temperature conditions.
However, in either the water bath 6 or the jacket type method, the temperature of the outside portion of the reactor 4 can easily be put in a low temperature condition, but the temperature of the central portion of the reactor 4 cannot easily reach the intended low temperature, thus causing there to be a temperature gradient in the fluid in the reactor 4.
Due to this phenomenon, it can be understood from tests for forming gas hydrates that a gas hydrate slurry forms only on the sidewall of the reactor 4 rather than in the central portion of the reactor 4.
As such, if a temperature gradient is caused in the reactor 4, the gas hydrate production rate is reduced.
Furthermore, when the temperature and pressure reach degrees that meet the formation conditions of gas hydrates, some water reacts with some gas to form gas hydrate slurry, but the remnants of water and gas stay in the reactor 4 without reacting with each other. The formed gas hydrate slurry contains a comparatively large amount of water therein, thus requiring a separate dehydration process.
Moreover, if water and gas which are used in the reaction just stay in the reactor 4, the processes of discharging only the formed gas hydrate slurry from the reactor 4 and re-supplying water and gas to compensate for the discharged amount of water and gas are repeated, thus reducing the rate at which gas hydrate is produced.